Hitherto, for simultaneously providing a long wear life and a high grip force, as shown in FIG. 2, what is called a SACT structure has been used for a tread section of a pneumatic radial tire for a motorcycle. In the SACT structure, a compound 21 having good wear resistance, having excellent durability, and having high rigidity is provided at a crown center section, and a soft compound 22 providing a high grip force is provided at a shoulder section. Higher speed of a vehicle in recent years has caused a demand for a tire having a high level high-speed durability. As a reinforcement layer, a mono-spiral belt having a reinforcement cord wound in a peripheral direction and having excellent high-speed durability is being used.
Regarding a tire in which a plurality of rubber types are used for tread rubber, for example, Patent Document 1 discloses a tire for a motorcycle. In the tire, a low-tan-δ tread rubber is disposed continuously from a tread center section through a carcass side of a shoulder section or discontinuously therefrom except for the shoulder section; and a high-tan-δ tread rubber is disposed at the shoulder section. Patent Document 2 discloses a pneumatic tire for a motorcycle. In the tire, a tread section, formed of two types of rubber, that is, hard rubber and soft rubber, is divided into three sections, that is, a center section and both shoulder sections; and the center section is formed of a single layer of hard rubber. In addition, each shoulder section has a cap-and-base structure in which the hard rubber forms a lower layer and the soft rubber forms an upper layer. Further, the thickness of the soft rubber at the center section is greater than the thickness at a side of an end of the tread section. Patent Document 3 discloses a tire for a motorcycle. In the tire, an inner layer, formed of bridged rubber having a high hardness, and an outer layer, formed of bridged rubber having a low hardness, are laminated upon each other at a shoulder section. In addition, a crown section is formed of bridged rubber having a high hardness.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 60-94804 (claims, etc.)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 11-189010 (claims, etc.)    Patent Document 3: Japanese Unexamined Patent Application Publication No. 2005-271760 (claims, etc.)